1. Field of the Invention
Multibeam electron guns, and, particularly, color television picture tube construction.
2. Prior Art
Multibeam electron guns especially those utilized in color television picture tubes having individual electrodes associated with the individual beam bundles having an aperture which permits the passage of the beams therethrough. The electrodes are mounted to supporting rods with the aid of suspension elements.
One such electron gun is disclosed in German Published Patent Application No. 25,11,758.
Experience has shown that there occurs a phenomenon which is called "convergence drifting" in a color television picture from a tube employing such an electron gun for example, during the transitional period starting at the time when the tube is put into operation until it reaches its working temperature.
Convergence drifting, as is well known, is due to the thermal expansion of the suspension elements in the electron gun which causes a change in the position of the beam passage opening, for example, that associated with the modulator electrodes. This thermal expansion of the suspension elements has a particular effect upon the electrodes lying outside the tube's axis. Because those electrodes, owing to their spatial conditions in the tube's neck, are mounted to the supporting rods which consist of an insulating material, for example, glass, in such a way that the thermal expansion of the susupension elements cannot be compensated for those electrodes which lie outside the tube's axis, whereas the electrode lying in the tube's axis is not a problem.
In the arrangements in accordance with the aforementioned German Published Patent Application No. 25,11,758, convergence drifting is attempted to be avoided or to be kept very small by selecting a material having a thermal coefficient of expansion which is as small as possible so that no visual faults or errors appear on the viewing screen.